The use of metallic electrodes provided with catalytic coatings in electrolytic applications is known in the art. Electrodes comprising a metal base (for instance made of titanium, zirconium or other valve metals, nickel, stainless steel, copper or alloys thereof) equipped with a coating based on noble metals or alloys thereof are, for instance, used as hydrogen-evolving cathodes in water or chlor-alkali electrolysis processes. In the case of cathodes for hydrogen electrolytic evolution, particularly relevant are coatings containing ruthenium, as metal or more frequently as ruthenium oxide, optionally in admixture with valve metal oxides. Electrodes of such kind may be produced by thermal processes, through the decomposition of precursor solutions of the metals to be deposited by suitable thermal treatments, or less frequently by galvanic electrodeposition from suitable electrolytic baths.
These preparation methods are capable of producing ruthenium catalysts characterised by a great variability of crystal lattice parameters, presenting a fair catalytic activity towards hydrogen evolution reaction, non perfectly correlated with the crystallite average size. The best catalysts produced by thermal decomposition of salt precursor solutions can, for instance, present a crystal average size of about 10-40 nm with a standard deviation of 2-3 nm, the relevant catalytic activity being moderately increased for samples at the lower end of the range.
In an industrial electrolytic process, the catalytic activity of the electrodes is directly reflected on the operating voltage of the electrolysers, and therefore on energy consumption. For this reason, it would be desirable to obtain catalysts with an increased activity towards gas evolution reactions, for instance towards the reaction of cathodic hydrogen evolution.